Overexpression of CD49f in precursor B-cell acute lymphoblastic leukemia: potential usefulness in minimal residual disease detection

The significance of CD49f expression in pediatric B-cell acute lymphoblastic leukemia

OBJECTIVES

CD49f is an adhesion molecule present on malignant lymphoblasts in B-cell acute lymphoblastic leukemia; it is associated with a poor prognosis. CD49f expression has been proposed as a marker for measurable residual disease (MRD) marker, but this marker has yet to be implemented in clinical practice.

METHODS

In this study, we used flow cytometry to detect CD49f expression by leukemic blasts in paired bone marrow and cerebrospinal fluid samples at diagnosis and bone marrow at day 15 of treatment.

RESULTS

At diagnosis, 93% of bone marrow and 100% of cerebrospinal fluid lymphoblasts expressed CD49f. The intensity of CD49f expression statistically significantly increased during treatment (P < .001). In MRD-negative end-of-treatment samples, only a small population of hematogones expressed CD49f. Interestingly, the intensity of CD49f expression varied among the different groups of recurrent genetic abnormalities. The ETV6::RUNX1 fusion and ETV6::RUNX1 combined with the high hyperdiploid group were associated with increased expression, whereas the Philadelphia-like group showed low CD49f expression. The lower CD49f expression at diagnosis predicted a lower MRD rate at day 15 of treatment.

CONCLUSIONS

We concluded that CD49f can be used as an MRD marker and possible prognostic factor in B-cell acute lymphoblastic leukemia.

Faster clinical decisions in B-cell acute lymphoblastic leukaemia: A single flow cytometric 12-colour tube improves diagnosis and minimal residual disease follow-up

Assessing minimal residual disease (MRD) in B-cell precursor acute lymphoblastic leukaemia (BCP-ALL) is essential for adjusting therapeutic strategies and predicting relapse. Quantitative polymerase chain reaction (qPCR) is the gold standard for MRD. Alternatively, flow cytometry is a quicker and cost-effective method that typically uses leukaemia-associated immunophenotype (LAIP) or different-from-normal (DFN) approaches for MRD assessment. This study describes an optimized 12-colour flow cytometry antibody panel designed for BCP-ALL diagnosis and MRD monitoring in a single tube. This method robustly differentiated hematogones and BCP-ALL cells using two specific markers: CD43 and CD81. These and other markers (e.g. CD73, CD66c and CD49f) enhanced the specificity of BCP-ALL cell detection. This innovative approach, based on a dual DFN/LAIP strategy with a principal component analysis method, can be used for all patients and enables MRD analysis even in the absence of a diagnostic sample. The robustness of our method for MRD monitoring was confirmed by the strong correlation (r = 0.87) with the qPCR results. Moreover, it simplifies and accelerates the preanalytical process through the use of a stain/lysis/wash method within a single tube (<2 h). Our flow cytometry-based methodology improves the BCP-ALL diagnosis efficiency and MRD management, offering a complementary method with considerable benefits for clinical laboratories.

Involvement of BCR::ABL1 in laminin adhesion of Philadelphia chromosome-positive acute lymphoblastic leukemia through upregulation of integrin α6

BACKGROUND

Adhesion of cancer cells to extracellular matrix laminin through the integrin superfamily reportedly induces drug resistance. Heterodimers of integrin α6 (CD49f) with integrin β1 (CD29) or β4 (CD104) are major functional receptors for laminin. Higher CD49f expression is reportedly associated with a poorer response to induction therapy in childhood B-cell precursor acute lymphoblastic leukemia (BCP-ALL). Moreover, a xenograft mouse model transplanted with primary BCP-ALL cells revealed that neutralized antibody against CD49f improved survival after chemotherapy.

AIMS

Considering the poor outcomes in Philadelphia chromosome (Ph)-positive ALL treated with conventional chemotherapy without tyrosine kinase inhibitors, we sought to investigate an involvement of the laminin adhesion.

METHODS AND RESULTS

Ph-positive ALL cell lines expressed the highest levels of CD49f among the BCP-ALL cell lines with representative translocations, while CD29 and CD104 were ubiquitously expressed in BCP-ALL cell lines. The association of Ph-positive ALL with high levels of CD49f gene expression was also confirmed in two databases of childhood ALL cohorts. Ph-positive ALL cell lines attached to laminin and their laminin-binding properties were disrupted by blocking antibodies against CD49f and CD29 but not CD104. The cell surface expression of CD49f, but not CD29 and CD104, was downregulated by imatinib treatment in Ph-positive ALL cell lines, but not in their T315I-acquired sublines. Consistently, the laminin-binding properties were disrupted by the imatinib pre-treatment in the Ph-positive ALL cell line, but not in its T315I-acquired subline.

CONCLUSION

BCR::ABL1 plays an essential role in the laminin adhesion of Ph-positive ALL cells through upregulation of CD49f.

Analytical Appraisal of Hematogones in B-ALL MRD Assessment Using Multidimensional Dot-Plots by Multiparametric Flow Cytometry: A Critical Review and Update

The spectrum of benign B-cell precursors, known as hematogones (HGs), shows a significant morphological and immunophenotypic overlap with their malignant counterpart i.e. B-lymphoid blasts (BLBs). This results in a diagnostic dilemma in assessment of cases wherein there is a physiological preponderance of HGs and also poses a significant challenge in measurable residual disease assessment in B-cell acute lymphoblastic leukaemia. Consequently, expression patterns of various immunophenotypic markers are considered the most important tool in identification and delineation of HGs from BLBs. However, certain aspects of B-cell compartment evaluation by flow cytometric immunophenotyping and its relevance in clinical scenarios is yet to be defined precisely. This review summarizes current flowcytometric data on HGs and its discrimination from BLBs based on thorough review of literature and evaluation of in-house data. Furthermore, it focuses on the utility of an additional analytical tool i.e., radar plot for a comprehensive representation of various subsets of the B-cell compartment and their differentiation from BLBs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12288-023-01696-5.

Regulation and Functions of α6-Integrin (CD49f) in Cancer Biology

Over the past decades, our knowledge of integrins has evolved from being understood as simple cell surface adhesion molecules to receptors that have a complex range of intracellular and extracellular functions, such as delivering chemical and mechanical signals to cells. Consequently, they actively control cellular proliferation, differentiation, and apoptosis. Dysregulation of integrin signaling is a major factor in the development and progression of many tumors. Many reviews have covered the broader integrin family in molecular and cellular studies and its roles in diseases. Nevertheless, further understanding of the mechanisms specific to an individual subunit of different heterodimers is more useful. Thus, we describe the current understanding of and exploratory investigations on the α6-integrin subunit (CD49f, VLA6; encoded by the gene itga6) in normal and cancer cells. The roles of ITGA6 in cell adhesion, stemness, metastasis, angiogenesis, and drug resistance, and as a diagnosis biomarker, are discussed. The role of ITGA6 differs based on several features, such as cell background, cancer type, and post-transcriptional alterations. In addition, exosomal ITGA6 also implies metastatic organotropism. The importance of ITGA6 in the progression of a number of cancers, including hematological malignancies, suggests its potential usage as a novel prognostic or diagnostic marker and useful therapeutic target for better clinical outcomes.

Class I Myosins, molecular motors involved in cell migration and cancer

Class I Myosins are a subfamily of motor proteins with ATPase activity and a characteristic structure conserved in all myosins: A N-Terminal Motor Domain, a central Neck and a C terminal Tail domain. Humans have eight genes for these myosins. Class I Myosins have different functions: regulate membrane tension, participate in endocytosis, exocytosis, intracellular trafficking and cell migration. Cell migration is influenced by many cellular components including motor proteins, like myosins. Recently has been reported that changes in myosin expression have an impact on the migration of cancer cells, the formation of infiltrates and metastasis. We propose that class I myosins might be potential markers for future diagnostic, prognostic or even as therapeutic targets in leukemia and other cancers.Abbreviations: Myo1g: Myosin 1g; ALL: Acute Lymphoblastic Leukemia, TH1: Tail Homology 1; TH2: Tail Homology 2; TH3: Tail Homology 3.

Pan-PI3Ki targets multiple B-ALL microenvironment interactions that fuel systemic and CNS relapse

The majority of adult patients with acute lymphoblastic leukemia (ALL) suffer relapse, and in patients with central nervous system (CNS) metastasis, prognosis is particularly poor. We recently demonstrated a novel route of ALL CNS metastasis dependent on PI3Kδ regulation of the laminin receptor integrin α6. B-ALL cells did not, however, rely on PI3Kδ signaling for growth. Here we show that broad targeting of PI3K isoforms can induce growth arrest in B-ALL, reducing systemic disease burden in mice treated with a single agent pan-PI3Ki, copanlisib. Moreover, we show that cellular stress activates PI3K/Akt-dependent survival pathways in B-ALL, exposing their vulnerability to PI3Kδ and pan-PI3Ki. The addition of a brief course of copanlisib to chemotherapy delivered the combined benefits of increased survival, decreased systemic disease, and reduced CNS metastasis. These data suggest the promising, multifaceted potential of pan-PI3Ki for B-ALL CNS prophylaxis, systemic disease control, and chemosensitization.

Leukaemia: a model metastatic disease

In contrast to solid cancers, which often require genetic modifications and complex cellular reprogramming for effective metastatic dissemination, leukaemic cells uniquely possess the innate ability for migration and invasion. Dedifferentiated, malignant leukocytes retain the benign leukocytes' capacity for cell motility and survival in the circulation, while acquiring the potential for rapid and uncontrolled cell division. For these reasons, leukaemias, although not traditionally considered as metastatic diseases, are in fact models of highly efficient metastatic spread. Accordingly, they are often aggressive and challenging diseases to treat. In this Perspective, we discuss the key molecular processes that facilitate metastasis in a variety of leukaemic subtypes, the clinical significance of leukaemic invasion into specific tissues and the current pipeline of treatments targeting leukaemia metastasis.

A cross-standardized flow cytometry platform to assess phenotypic stability in precursor B-cell acute lymphoblastic leukemia (B-ALL) xenografts

With the continued poor outcome of relapsed acute lymphoblastic leukemia (ALL), new patient‐specific approaches for disease progression monitoring and therapeutic intervention are urgently needed. Patient‐derived xenografts (PDX) of primary ALL in immune‐deficient mice have become a powerful tool for studying leukemia biology and therapy response. In PDX mice, the immunophenotype of the patient's leukemia is commonly believed to be stably propagated. In patients, however, the surface marker expression profile of the leukemic population often displays poorly understood immunophenotypic shifts during chemotherapy and ALL progression. We therefore developed a translational flow cytometry platform to study whether the patient‐specific immunophenotype is faithfully recapitulated in PDX mice. To enable valid assessment of immunophenotypic stability and subpopulation complexity of the patient's leukemia after xenotransplantation, we comprehensively immunophenotyped diagnostic B‐ALL from children and their matched PDX using identical, clinically standardized flow protocols and instrument settings. This cross‐standardized approach ensured longitudinal stability and cross‐platform comparability of marker expression intensity at high phenotyping depth. This analysis revealed readily detectable changes to the patient leukemia‐associated immunophenotype (LAIP) after xenotransplantation. To further investigate the mechanism underlying these complex immunophenotypic shifts, we applied an integrated analytical approach that combined clinical phenotyping depth and high analytical sensitivity with unbiased high‐dimensional algorithm‐based analysis. This high‐resolution analysis revealed that xenotransplantation achieves patient‐specific propagation of phenotypically stable B‐ALL subpopulations and that the immunophenotypic shifts observed at the level of bulk leukemia were consistent with changes in underlying subpopulation abundance. By incorporating the immunophenotypic complexity of leukemic populations, this novel cross‐standardized analytical platform could greatly expand the utility of PDX for investigating ALL progression biology and assessing therapies directed at eliminating relapse‐driving leukemic subpopulations.

Integrin α6 mediates the drug resistance of acute lymphoblastic B-cell leukemia

Resistance to multimodal chemotherapy continues to limit the prognosis of acute lymphoblastic leukemia (ALL). This occurs in part through a process called adhesion-mediated drug resistance, which depends on ALL cell adhesion to the stroma through adhesion molecules, including integrins. Integrin α6 has been implicated in minimal residual disease in ALL and in the migration of ALL cells to the central nervous system. However, it has not been evaluated in the context of chemotherapeutic resistance. Here, we show that the anti-human α6-blocking Ab P5G10 induces apoptosis in primary ALL cells in vitro and sensitizes primary ALL cells to chemotherapy or tyrosine kinase inhibition in vitro and in vivo. We further analyzed the underlying mechanism of α6-associated apoptosis using a conditional knockout model of α6 in murine BCR-ABL1+ B-cell ALL cells and showed that α6-deficient ALL cells underwent apoptosis. In vivo deletion of α6 in combination with tyrosine kinase inhibitor (TKI) treatment was more effective in eradicating ALL than treatment with a TKI (nilotinib) alone. Proteomic analysis revealed that α6 deletion in murine ALL was associated with changes in Src signaling, including the upregulation of phosphorylated Lyn (pTyr507) and Fyn (pTyr530). Thus, our data support α6 as a novel therapeutic target for ALL.

Monitoring minimal/measurable residual disease in B-cell acute lymphoblastic leukemia by flow cytometry during targeted therapy

B-cell acute lymphoblastic leukemia (B-ALL) is a hematologic malignancy of B-type lymphoid precursor cells. Minimal/measurable residual disease (MRD) is an important prognostic factor for B-ALL relapse. Traditional flow cytometry detection mainly relies on CD19-based gating strategies. However, relapse of CD19-negative B-ALL frequently occurs in patients who receive cellular and targeted therapy. This review will summarize the technical aspects of standard MRD assessment in B-ALL by flow cytometry, and then discuss the challenges of MRD strategies to deal with the scenario of CD19 negative or dim B-ALL relapse.

Cadherins, Selectins, and Integrins in CAM-DR in Leukemia

The interaction between leukemia cells and the bone microenvironment is known to provide drug resistance in leukemia cells. This phenomenon, called cell adhesion-mediated drug resistance (CAM-DR), has been demonstrated in many subsets of leukemia including B- and T-acute lymphoblastic leukemia (B- and T-ALL) and acute myeloid leukemia (AML). Cell adhesion molecules (CAMs) are surface molecules that allow cell-cell or cell-extracellular matrix (ECM) adhesion. CAMs not only recognize ligands for binding but also initiate the intracellular signaling pathways that are associated with cell proliferation, survival, and drug resistance upon binding to their ligands. Cadherins, selectins, and integrins are well-known cell adhesion molecules that allow binding to neighboring cells, ECM proteins, and soluble factors. The expression of cadherin, selectin, and integrin correlates with the increased drug resistance of leukemia cells. This paper will review the role of cadherins, selectins, and integrins in CAM-DR and the results of clinical trials targeting these molecules.

The extracellular matrix: A key player in the pathogenesis of hematologic malignancies

Hematopoietic stem and progenitor cells located in the bone marrow lay the foundation for multiple lineages of mature hematologic cells. Bone marrow niches are architecturally complex with specific cellular, physiochemical, and biomechanical factors. Increasing evidence suggests that the bone marrow microenvironment contributes to the pathogenesis of hematological neoplasms. Numerous studies have deciphered the role of genetic mutations and chromosomal translocations in the development hematologic malignancies. Significant progress has also been made in understanding how the cellular components and cytokine interactions within the bone marrow microenvironment promote the evolution of hematologic cancers. Although the extracellular matrix is known to be a key player in the pathogenesis of various diseases, it's role in the progression of hematologic malignancies is less understood. In this review, we discuss the interactions between the extracellular matrix and malignant cells, and provide an overview of the role of extracellular matrix remodeling in sustaining hematologic malignancies.

Measurable residual disease of acute lymphoblastic leukemia in allograft settings: how to evaluate and intervene

INTRODUCTION

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains a curable strategy for acute lymphoblastic leukemia (ALL), especially for adult cases. However, leukemia relapse after allograft restricts the improvement of transplant outcomes. Measurable residual disease (MRD) has been the strongest predictor for relapse after allo-HSCT, allowing MRD-directed preemptive therapy.

AREAS COVERED

This manuscript summarizes the detection of MRD in patients with ALL who undergo allo-HSCT, focusing the effects of positive pre-HSCT MRD and post-HSCT MRD on outcomes as well as MRD-directed interventions.

EXPERT OPINION

Except for MFC and RQ-PCR, other strategies, such as next-generation sequencing and RNAseq, have been developed for MRD determination. Negative effects of positive MRD peri-transplantation on outcomes of ALL patients were observed both in human leukocyte antigen (HLA)-matched sibling donor transplantation and in alternative donor transplantation. Advances have been made in determining the need for transplant according to MRD evaluation after induction or consolidation therapy. A number of approaches, including CAR-T-cell therapy, antibodies (blinatumomab, etc), targeted therapy (imatinib, etc), transplant donor selection, as well as donor lymphocyte infusion and interferon-α, have been successfully used or are promising for peri-transplantation MRD interventions. This progress could lead to the significant improvement of transplant outcomes for ALL patients.

Integrin-Mediated Adhesion and Chemoresistance of Acute Lymphoblastic Leukemia Cells Residing in the Bone Marrow or the Central Nervous System

Acute Lymphoblastic Leukemia (ALL) is the most common cancer in childhood. Despite a significantly improved prognosis over the last decade with a 5-years survival rate of ~90%, treatment-related morbidity remains substantial and relapse occurs in 10–15% of patients (1). The most common site of relapse is the bone marrow, but early colonization and subsequent reoccurrence of the disease in the central nervous system (CNS) also occurs. Integrins are a family of cell surface molecules with a longstanding history in cancer cell adherence, migration and metastasis. In chronic lymphoblastic leukemia (CLL), the VLA-4 integrin has been acknowledged as a prognostic marker and mounting evidence indicates that this and other integrins may also play a role in acute leukemia, including ALL. Importantly, integrins engage in anti-apoptotic signaling when binding extracellular molecules that are enriched in the bone marrow and CNS microenvironments. Here, we review the current evidence for a role of integrins in the adherence of ALL cells within the bone marrow and their colonization of the CNS, with particular emphasis on mechanisms adding to cancer cell survival and chemoresistance.

Flow Cytometric Minimal Residual Disease Analysis in Acute Leukemia: Current Status

Minimal residual disease (MRD) analysis for patients of acute leukemia has evolved as a significant prognostic factor. Based on the MRD results, the cases are risk-stratified after induction chemotherapy, and an alteration in further management is made to yield maximal therapeutic benefits. The two primary methodologies for MRD detection are multi-parameter flow cytometry (MFC) and polymerase chain reaction. MFC identifies the MRD based on characteristic 'leukemia-associated immunophenotypes' on the residual leukemia cells. MRD analysis by MFC is most frequently done at the post-induction stage of treatment and often can achieve a sensitivity of detecting one leukemic cell in 10,000 normal cells, or even higher at times. This review outlines the technical aspects and provides inputs on standard antibody panels used for MRD detection in B-, T-lineage acute lymphoblastic leukemias, and acute myeloid leukemia.

Immunophenotyping of Acute Lymphoblastic Leukemia

Immunophenotyping by flow cytometry is an important component in the diagnostic evaluation of patients with acute lymphoblastic leukemia. This technique further permits the detection of minimal residual disease after therapy, a robust prognostic factor that may guide individualized treatment. We describe here laboratory methods for both the initial characterization of lymphoblasts at diagnosis, and the detection of rare leukemic lymphoblasts after treatment. In addition to antibody combinations suitable for diagnosis and detection of minimal residual disease, we describe procedures for peripheral blood and bone marrow sample preparation, procedures for labeling of cell-surface and intracellular proteins with fluorochrome-conjugated antibodies, and approaches to analysis of immunophenotypic data.

PhenoGraph and viSNE facilitate the identification of abnormal T-cell populations in routine clinical flow cytometric data

BACKGROUND

Flow cytometric identification of neoplastic T-cell populations is complicated by the wide range of phenotypic abnormalities in T-cell neoplasia, and the diverse repertoire of reactive T-cell phenotypes. We evaluated whether a recently described clustering algorithm, PhenoGraph, and dimensionality-reduction algorithm, viSNE, might facilitate the identification of abnormal T-cell populations in routine clinical flow cytometric data.

METHODS

We applied PhenoGraph and viSNE to peripheral blood mononuclear cells labeled with a single 8-color T/NK-cell antibody combination. Individual peripheral blood samples containing either a T-cell neoplasm or reactive lymphocytosis were analyzed together with a cohort of 10 normal samples, which established the location and identity of normal mononuclear-cell subsets in viSNE displays.

RESULTS

PhenoGraph-derived subpopulations from the normal samples formed regions of phenotypic similarity in the viSNE display describing normal mononuclear-cell subsets, which correlated with those obtained by manual gating (r²  = 0.99, P < 0.0001). In 24 of 24 cases of T-cell neoplasia with an aberrant phenotype, compared with 4 of 17 cases of reactive lymphocytosis (P = 1.4 × 10^-7 , Fisher Exact test), PhenoGraph-derived subpopulations originating exclusively from the abnormal sample formed one or more distinct phenotypic regions in the viSNE display, which represented the neoplastic T cells, and reactive T-cell subpopulations not present in the normal cohort, respectively. The numbers of neoplastic T cells identified using PhenoGraph/viSNE correlated with those obtained by manual gating (r²  = 0.99; P < 0.0001).

CONCLUSIONS

PhenoGraph and viSNE may facilitate the identification of abnormal T-cell populations in routine clinical flow cytometric data. © 2017 Clinical Cytometry Society.

Early recovery of circulating immature B cells in B-lymphoblastic leukemia patients after CD19 targeted CAR T cell therapy: A pitfall for minimal residual disease detection

BACKGROUND

CD19-targeted chimeric-antigen receptor-modified T-cells (CAR-T) are promising in the treatment of refractory B-lymphoblastic leukemia (B-ALL). Minimal residual disease (MRD) detection by multicolor flow cytometry (FCM) is critical to distinguish B-ALL MRD from regenerating, non-neoplastic B-cell populations.

METHODS

FCM was performed on samples from 9 patients with B-ALL treated with CAR-T.

RESULTS

All 9 patients showed response to CAR-T. Additionally, FCM revealed circulating CD10 + B cells, potentially mimicking MRD. Circulating CD10+ B-cells were detected in blood from 3 days to 3 months after CAR-T, comprising 73% (median) of B-cells (52-83%, 95%CI). They expressed CD19, CD10, CD20, bright CD9, CD22, CD24, moderate CD38 and dim CD58, but were CD34 (-), with bright CD45 and polyclonal surface light chain immunoglobulin (sIg) expression. A similar CD10 + B-cell subpopulation was detected by marrow FCM, amidst abundant B-cell precursors.

CONCLUSIONS

These circulating CD10 + B-cells are compatible with immature B-cells, and are a reflection of B-cell recovery within the marrow. They are immunophenotypically distinguishable from residual B-ALL. Expression of light chain sIg and key surface antigens characterizing regenerating B-cell precursors can distinguish immature B-cells from B-ALL MRD and prevent misdiagnosis. © 2017 International Clinical Cytometry Society.

Current Strategies for the Detection of Minimal Residual Disease in Childhood Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) is the most common cancer in children. Current treatment strategies for childhood ALL result in long-term remission for approximately 90% of patients. However, the therapeutic response is worse among those who relapse. Several risk stratification approaches based on clinical and biological aspects have been proposed to intensify treatment in patients with high risk of relapse and reduce toxicity on those with a greater probability of cure.

The detection of residual leukemic cells (minimal residual disease, MRD) is the most important prognostic factor to identify high-risk patients, allowing redefinition of chemotherapy. In the last decades, several standardized research protocols evaluated MRD using immunophenotyping by flow cytometry and/or real-time quantitative polymerase chain reaction at different time points during treatment. Both methods are highly sensitive (10⁻³ a 10⁻⁵), but expensive, complex, and, because of that, require qualified staff and frequently are restricted to reference centers.

The aim of this article was to review technical aspects of immunophenotyping by flow cytometry and real-time quantitative polymerase chain reaction to evaluate MRD in ALL.

The application of CD73 in minimal residual disease monitoring using flow cytometry in B-cell acute lymphoblastic leukemia

The expression of CD73 by flow cytometry (FC) in bone marrow (BM) specimens of B-cell acute lymphoblastic leukemia (B-ALL) with or without minimal residual disease (MRD) was studied, and its advantages were evaluated using the MRD assay. This study also detected the expression profile of CD73 in hematogones and mature B cells in BM specimens of 18 healthy donors. Results showed that the mean value of CD73 expression in MRD-positive B cells was 6-fold greater than that in the MRD negative ones. Also, 41.82% MRD-positive B-ALL cases expressed high CD73 and the sensitivity of CD73-based MRD detection reached 10(-4). Since the expression of CD73 increases with the maturation of normal B cells, it is better to mix it with CD34, CD10 and CD20 in one tube to prevent the disturbance of mature B cells. CD73 is recommended as an optional MRD marker for B-ALL patients by using FC.

Detection of minimal residual disease in B lymphoblastic leukemia using viSNE

BACKGROUND

Minimal residual disease (MRD) following treatment is a robust prognostic marker in B lymphoblastic leukemia. However, the detection of MRD by flow cytometric immunophenotyping is technically challenging, and an automated method to detect MRD is therefore desirable. viSNE, a recently developed computational tool based on the t-Distributed Stochastic Neighbor Embedding (t-SNE) algorithm, has been shown to be capable of detecting synthetic "MRD-like" populations of leukemic cells created in vitro, but whether viSNE can facilitate the immunophenotypic detection of MRD in clinical samples has not been evaluated.

METHODS

We applied viSNE retrospectively to 8-color flow cytometric immunophenotyping data from normal bone marrow samples, and samples from B lymphoblastic leukemia patients with or without suspected MRD on the basis of conventional manual gating.

RESULTS

In each of 14 bone marrow specimens containing MRD or suspected MRD, viSNE identified a putative MRD population; an abnormal composite immunophenotype was confirmed for the putative MRD in each case. MRD populations were not identified by viSNE in control bone marrow samples from patients with increased normal B-cell precursors, or in post-treatment samples from B lymphoblastic leukemia patients who did not have detectable MRD by manual gating.

CONCLUSION

viSNE shows promise as an automated method to facilitate immunophenotypic MRD detection in patients treated for B lymphoblastic leukemia.

Identifying new targets in leukemogenesis using computational approaches

There is a need to identify novel targets in Acute Lymphoblastic Leukemia (ALL), a hematopoietic cancer affecting children, to improve our understanding of disease biology and that can be used for developing new therapeutics. Hence, the aim of our study was to find new genes as targets using in silico studies; for this we retrieved the top 10% overexpressed genes from Oncomine public domain microarray expression database; 530 overexpressed genes were short-listed from Oncomine database. Then, using prioritization tools such as ENDEAVOUR, DIR and TOPPGene online tools, we found fifty-four genes common to the three prioritization tools which formed our candidate leukemogenic genes for this study. As per the protocol we selected thirty training genes from PubMed. The prioritized and training genes were then used to construct STRING functional association network, which was further analyzed using cytoHubba hub analysis tool to investigate new genes which could form drug targets in leukemia. Analysis of the STRING protein network built from these prioritized and training genes led to identification of two hub genes, SMAD2 and CDK9, which were not implicated in leukemogenesis earlier. Filtering out from several hundred genes in the network we also found MEN1, HDAC1 and LCK genes, which re-emphasized the important role of these genes in leukemogenesis. This is the first report on these five additional signature genes in leukemogenesis. We propose these as new targets for developing novel therapeutics and also as biomarkers in leukemogenesis, which could be important for prognosis and diagnosis.

Detection of small abnormal B-Lymphoblast populations at diagnosis of chronic myelogenous leukemia, BCR-ABL1+: Incidence, phenotypic features, and clinical implications

BACKGROUND

According to the 2008 World Health Organization (WHO) Classification of Tumors of the Haematopoietic and Lymphoid Tissues, the finding of B lymphoblasts in the blood or bone marrow of a patient with chronic myelogenous leukemia, BCR-ABL1+ (CML) should raise a concern for progression of the disease to B-lymphoblastic blast phase. Data addressing the incidence and phenotypic features of abnormal B lymphoblasts in CML, and whether the detection of B lymphoblasts inexorably heralds blast phase in CML, though, are limited.

METHODS

We reviewed a consecutive series of patients with newly diagnosed CML who had undergone bone marrow examination with flow cytometric immunophenotyping. Polychromatic immunophenotyping data were reviewed, and clinical follow-up data were obtained.

RESULTS

A precursor B-cell population with an abnormal composite immunophenotype was detected in 4 of 36 (11.1%) diagnostic bone marrow samples, at levels ranging from 0.01% to 0.30% of viable single cells acquired. The most common phenotypic aberrations were abnormally bright expression of CD10 and CD19 (seen in four and three cases, respectively), and abnormally dim expression of CD38 (seen in four cases). All three patients with adequate clinical follow-up have achieved and maintained a deep or major molecular response with a tyrosine kinase inhibitor, and none has progressed to B-lymphoblastic blast phase (follow-up duration: 17-46 months).

CONCLUSIONS

In chronic-phase CML, a small (<0.5%) abnormal B-lymphoblast population is present in a significant minority of diagnostic bone marrow samples, but does not inevitably herald progression to B-lymphoblastic blast phase. © 2015 International Clinical Cytometry Society.

Obesity is associated with residual leukemia following induction therapy for childhood B-precursor acute lymphoblastic leukemia

Obesity is associated with poorer event-free survival (EFS) in pediatric acute lymphoblastic leukemia (ALL). Persistent minimal residual disease (MRD) in the bone marrow as measured by multidimensional flow cytometry (MDF) is a key early prognostic indicator and is strongly associated with EFS. We therefore hypothesized that obesity during induction would be associated with positive end-of-induction MRD (≥0.01%). We analyzed MDF of end-induction bone marrow samples from a historical cohort of 198 children newly diagnosed with B-precursor ALL (BP-ALL) and treated with Children's Oncology Group induction regimens. We assessed the influence of body mass index on risk for positive end-induction MRD in the bone marrow. In our cohort of BP-ALL, 30 children (15.2%) were overweight and 41 (20.7%) were obese at diagnosis. Independent of established predictors of treatment response, obesity during induction was associated with significantly greater risk for persistent MRD (odds ratio, 2.57; 95% confidence interval, 1.19 to 5.54; P = .016). Obesity and overweight were associated with poorer EFS irrespective of end-induction MRD (P = .012). Obese children with newly diagnosed BP-ALL are at increased risk for positive end-induction MRD and poorer EFS.

Minimal residual disease in acute lymphoblastic leukemia: optimal methods and clinical relevance, pitfalls and recent approaches

After advances in experimental and clinical testing, minimal residual disease (MRD) assay results are considered a determining factor in treatment of acute lymphoblastic leukemia patients. According to MRD assay results, bone marrow (BM) leukemic burden and the rate of its decline after treatment can be directly evaluated. Detailed knowledge of the leukemic burden in BM can minimize toxicity and treatment complications in patients by tailoring the therapeutic dose based on patients' conditions. In addition, reduction of MRD before allo-HSCT is an important prerequisite for reception of transplant by the patient. In direct examination of MRD by morphological methods (even by a professional hematologist), leukemic cells can be under- or over-estimated due to similarity with hematopoietic precursor cells. As a result, considering the importance of MRD, it is necessary to use other methods including flow cytometry, polymerase chain reaction (PCR) amplification and RQ-PCR to detect MRD. Each of these methods has its own advantages and disadvantages in terms of accuracy and sensitivity. In this review article, different MRD assay methods and their sensitivity, correlation of MRD assay results with clinical symptoms of the patient as well as pitfalls in results of these methods are evaluated. In the final section, recent advances in MRD have been addressed.

New markers for minimal residual disease detection in acute lymphoblastic leukemia

To identify new markers for minimal residual disease (MRD) detection in acute lymphoblastic leukemia (ALL), we compared genome-wide gene expression of lymphoblasts from 270 patients with newly diagnosed childhood ALL to that of normal CD19⁺CD10⁺ B-cell progenitors (n = 4). Expression of 30 genes differentially expressed by ≥ 3-fold in at least 25% of cases of ALL (or 40% of ALL subtypes) was tested by flow cytometry in 200 B-lineage ALL and 61 nonleukemic BM samples, including samples containing hematogones. Of the 30 markers, 22 (CD44, BCL2, HSPB1, CD73, CD24, CD123, CD72, CD86, CD200, CD79b, CD164, CD304, CD97, CD102, CD99, CD300a, CD130, PBX1, CTNNA1, ITGB7, CD69, CD49f) were differentially expressed in up to 81.4% of ALL cases; expression of some markers was associated with the presence of genetic abnormalities. Results of MRD detection by flow cytometry with these markers correlated well with those of molecular testing (52 follow-up samples from 18 patients); sequential studies during treatment and diagnosis-relapse comparisons documented their stability. When incorporated in 6-marker combinations, the new markers afforded the detection of 1 leukemic cell among 10(5) BM cells. These new markers should allow MRD studies in all B-lineage ALL patients, and substantially improve their sensitivity.

Immunologic minimal residual disease detection in acute lymphoblastic leukemia: a comparative approach to molecular testing

The generation of antisera directed against leukocyte differentiation antigens opened the possibility of studying minimal residual disease (MRD) in patients with acute lymphoblastic leukemia (ALL). During the three decades that followed the pioneering studies in this field, great progress has been made in the development of a wide array of monoclonal antibodies and of flow cytometric techniques for rare event detection. This advance was accompanied by an increasingly greater understanding of the immunophenotypic features of leukemic and normal lymphoid cells, and of the antigenic differences that make MRD studies possible. In parallel, molecular methods for MRD detection were established. The systematic application of immunologic and molecular techniques to study MRD in clinical samples has demonstrated the clinical significance of MRD in patients, leading to the use of MRD to regulate treatment intensity in many contemporary protocols. In this article, we discuss methodologic issues related to the immunologic monitoring of MRD and the evidence supporting its clinical significance, and compare the advantages and limitations of this approach to those of molecular monitoring of MRD.